Why do all Windows have the same style? Why is there no variety. On Windows front u have no choice but to live with the Windows UI that microsoft gives you, whether you like it or not. What if you wanted to use the Macintosh UI? U have no choice. On the contrary there are so many GUI projects in the UNIX world that I can explain only a few of the most remarkable ones.
One of the earlier ones were designed to work with very limited resources. For people who want a Windows 95 like interface there is FVWM(F? Virtual Window Manager). Sorry.. Do not ask me what F stands for. The original Author, Rob Nation himself forgot what it originally stood for. But I am asuming F stood for FVWM just like GNU stands for GNU is Not Unix. It was developed as an improvement to otherwise ugly twm. The screenshot showed here is the very minimalistic FVWM2 interface. No themes at all. Click it for a bigger view. Or visit the fvwm official site http://www.fvwm.org for more screenshots and really cool ones.
Another interesting Interface was called WindowMaker. I say "was called" because due to some naming issues it was sued by a company making Windows and Doors and they changed the name to Window Maker to relate it to the X-Window process in which it creates windows. This was the first interface I used on Linux and it was very simple, very light weight(used on a machine with 8MB RAM) and very different. It does not have a start menu. But it does have a nicely hidden application menu where all the apps reside. To get this you just have to right click on the desktop. I experimented with this and designed three themes for it. Just search my name, Sam Albuquerque, on Google and you will find the first link pointing to these themes that I designed myself. For direct access click this link http://themes.freshmeat.net/~albuquerque/
If you like the XP look and feel there is another project called the XPde(XP Desktop Environment). The aim of the XPde project is to make it easier for XP users to migrate to Linux. Just have a look at the screenshots at http://www.xpde.com, the official Website of XPde. They have managed to get many of the XP features into xpde. The ALT+TAB works similar to Xp, the strat menu is similar to that of XP, etc.
There are many such Interfaces. But two major environments on which many such interfaces work are the GNOME and the KDE. GNOME stands for the GNU Network Object Model Environment. GNOME is usually distributed by almost every distribution of Linux. It was started as an answer to KDE because KDE used a set of libraries which at the time of its conception was not free. The Qt libraries which KDE used was then made free by Trolltech. However, GNOME and KDE evolved out as two string projects with lots of wonderful features and applications developed. Both of them have their own office suites too. Visit http://www.gnome.org for details on the GNOME project and to see a lot of their screenshots.
KDE can be accessed at http://www.kde.org. KDE was started with a view to bring some consistency in the Unix applications of the time since all applications had its own look and feel. Matthias Ettrich, who started the KDE project was concerned that his girlfriend was having difficulty in using his desktop. He started developing a complete desktop environment by using the Qt libraries and other programmers joined his bandwagon. There was initial concerns which spurred the GNOME movement. But Trolltech finally made its source code open under the GPL and now there are no issues at all. So finally everyone loves Konqi the friendly dragon.
Allow me to make you a bit more jealous. Does your Windows support 3d desktop? Our cute little Linux supports a fantastic 3D desktop using XGL Cube. Its sexy, it superb and its WOW!! I wont say more now but let you watch for yourself the power of linux with this XGL video..